In Cisco IOS Software Release 12.1(20)E and later, the support for disablement of IP routing has been removed for Catalyst 6500 series switches. You cannot disable IP routing in these switches, as this example shows: Cat6500(config)#no ip routing ...

It depends on what supervisor is installed in 4510. Which line cards do you have in 4510? What configuration of 3750 you have? Do they have a 10G ethernet port?

Try "no vlan DOt1q tag native" command.

I think the better way to communicate 2 server with ecah other at L3 is to place them in seperate vlans. Is it possible in IP configuration?